When given orally for 1 month (5 days/week, 22 total doses) to Fischer 344 rats, the LD50 (90-day observation) was estimated to be 65 mg/kg/day (total 1.43 gm/kg) for the female rat and 149 mg/kg/day (total 3.28 gm/kg) for the male. All female rats given 22 doses at 100 mg/kg/day (total 2.20 gm/kg) died between 41 and 53 days while only 38% of the males died between 50 and 73 days. Pathologic changes in treated rats were enlargement of the liver with accentuation of the hepatic lobular markings and atrophy of thymus and spleen. Microscopically, hepatic changes were characterized by congestion, fatty infiltration, and multifocal liquefactive characterized by congestion, fatty infiltration, and multifocal liquefactive necrosis. Male rats given 100 mg/kg/day and dying after 90 days had subacute to chronic hepatitis with marked focal proliferation of bile ducts.